The invention relates generally to an internal permanent magnet machine and more particularly, to a high-speed internal permanent magnet machine with high power-density.
Internal Permanent Magnet (IPM) Machines such as IPM motors or generators have been widely used in a variety of applications including aircraft, automobiles and industrial usage. However, IPM machines are currently the clear favorite in hybrid automotive applications. Therefore, a requirement for lightweight and high power density IPM machines has resulted in the design of higher speed motors and generators to maximize the power to weight ratios. Hence, the trend is increasing acceptance of IPM machines offering high machine speed, high power density, reduced mass and cost. In a conventional IPM machine, multiple permanent magnets are embedded inside multiple laminations of a rotor. The mechanical stresses in the rotor are concentrated in multiple bridges and center posts. For higher speed applications, the thickness of the multiple bridges and center posts have to be increased for enhanced structural strength of the rotor and various other parts. The increased thickness leads to more magnet flux leakage into the multiple bridges and center posts, which leakage significantly reduces the machine power density, resulting in decreased efficiency of the machine.
Therefore, it is desirable to have a high-speed IPM machine with high power density and efficiency.